Heretofore, as a technique of the above type, there is known an exhaust gas heat-exchanger disclosed in Patent Literature 1 mentioned below. FIG. 10 is a cross sectional view of part of this heat-exchanger. This heat-exchanger includes a hollow shell 61 having an internal space and an exhaust gas manifold 62 fixed at one end of the shell 61. The exhaust gas manifold 62 includes a first exhaust gas chamber 64 and a second exhaust gas chamber 65 adjacent to each other with a baffle plate 63 interposed therebetween. The exhaust gas chamber 64 includes an exhaust gas inlet 66 and the exhaust gas chamber 65 includes an exhaust gas outlet 67, respectively. The first and second exhaust chambers 64 and 65 are partitioned by the baffle plate 63 and a flap valve element 68. The flap valve element 68 is placed to be rotatable at its one end about a pin 69. As shown by a solid line in FIG. 10, while the flap valve element 68 is placed in a closed position to close an opening 70 of the baffle plate 63, exhaust gas flowing in the first exhaust gas chamber 64 is allowed to flow into the shell 61 and then flow into the second exhaust gas chamber 65 via the shell 61 without directly flowing into the second exhaust gas chamber 65. On the other hand, as shown by a broken line in FIG. 10, while the flap valve element 68 is placed to open the opening 70, the exhaust gas flowing in the first exhaust gas chamber 64 is allowed to directly flow into the second exhaust gas chamber 65. As above, a flow direction of the exhaust gas is switched between a flow direction passing through the shell 61 and a flow direction not passing through the shell 61.